of some Siliceoua Sandstones. 301 



the sand of the loose sandstone is found to have a different 

 character when compared with the sand of the compact stone ; 

 one is seen to be water-worn, even the minute crystals of 

 quartz which may be occasionally observed ; the other is found 

 without marks of being water-worn, the grains with sharp 

 edges and angles, and many of them crystalline. When 

 fragments of the two different sandstones are similarly ex- 

 amined, the loosely-cohering one exhibits the water-worn 

 grains separated by matter in a much finer state, of chalk- 

 like appearance ; whilst the compact one displays the angu- 

 lar sharp-edged crystalline grains in contact, and as it were 

 entangled, without any finer granular matter intervening. 



Does not, then, the cause of the difference under consider- 

 ation, exist in the circumstances which the microscope brings 

 to light? Is not the compactness of the Edinburgh stone 

 owing to its being crystalline, the crystalline grains ad- 

 hering together % Is not the looseness and want of cohesion, 

 under water, of the Barbadoes stone, owing to its grains hav- 

 ing been all deposited water-worn, without any crystalline ce- 

 ment, and having interposed a finer granular matter, a kind 

 of clay, absorbent of and yielding to w^ater ? 



I have said that these two sandstones belong apparently 

 to analogous formations. Perhaps, farther inquiry may prove 

 that whilst the crystalline rock is of the group of the old red 

 sandstones, the other, without a crystalline siliceous cement, 

 belongs to one of more recent origin, — or the group of new 

 red sandstones. 



Though most of the sandstones of this island are of the 

 character pointed out, there are exceptions, — indeed in the 

 district referred to, as regards the equality of firmness, a 

 complete gradation is often observable from loose uncoher- 

 ing sand to compact sandstone, and that in contiguous strata. 

 A hill near " Chalky Mount" consists of such strata; here 

 may be seen a layer of loose siliceous sand, resting on a thin 

 stratum of loose sandstone, and covered by one that is com- 

 pact, and this to the extent of many alternations. Where 

 there is any compactness in these strata, they are found to 

 owe it either to carbonate of lime, or to peroxide of iron, or 



